Like the Renaissance, which slighly predates it, the Reformation has a multitude of possible starting points. The wish to rediscover a simpler and more authentic version of the Christian life is characteristic of many new movements within Christianity, one of which is the commitment to poverty of St Francis. Reaction against the worldliness of the church is another recurrent theme, as in the case of Savonarola.

But John Wycliffe, in 14th century England, introduces so many strands of the Reformation - in relation to worldly prelates, the primacy of scripture and the nature of the eucharist - that he is usually identified as the main precursor of this greatest of all upheavals in Christian history.

Wycliffe's heresies: 1376-1395

Between 1376 and 1379 John Wycliffe, writing mainly in Oxford, takes a controversial line on a great many issues. He argues that the church has no proper role in temporal matters and that corrupt churchmen lose even the spiritual authority supposedly attached to their office. He maintains that all a Christian needs is the example of scripture, which believers should be able to read in their own languages. He denies that the consecrated bread and wine are literally transubstantiated into the body and blood of Christ.

Most provocative of all, he can find no justification in scripture for the authority of the pope.

In 1377 pope Gregory XI orders Wycliffe to be imprisoned and examined, but he has powerful protectors in England (including John of Gaunt). He is placed briefly under house arrest. In 1378 Gregory XI dies and the papacy is plunged into its Great Schism. Two rival popes have more pressing matters on hand than the English heretic. Wycliffe retires to spend the last few years of his life in the parish of Lutterworth, where he dies in 1384.

His ideas are spread in England by followers who become known as the Lollards (from a Dutch word for a 'mutterer'). Lollard attitudes - more strident than Wycliffe's, and expressed in a more popular manner - prefigure much that will be associated with puritanism.

Central to the Lollard programme are two Wycliffite themes - that the main task of a priest is to preach, and that the scriptures should be accessible to everyone. He would also have approved of their scornful dismissal of Rome's pretensions. But the Twelve Conclusions, drawn up by Lollards in 1395, go considerably further - finding fault with images, pilgrimage, vestments, confession, the celibacy of priests and even the vows of chastity taken by nuns.

As a persecuted sect, the Lollards play only a small role in 15th century England. But the works of Wycliffe, carried from Oxford to Prague, ferment powerful unrest among the followers of John Huss.

The Bethlehem Chapel and John Huss: 1402-1414

John Huss, a teacher of philosophy in Prague university, is appointed in 1402 to a controversial position. He is put in charge of the Bethlehem chapel in Prague.

The chapel, founded about ten years previously, is associated with a radical approach to Christianity. The pulpit here is as prominent a feature as the altar. It is to be a place for sermons in the Czech language, comprehensible to ordinary people. The preachers argue for a simple Christianity, a religion of poverty and humility, very different from the worldly grandeur of the papacy.

At about the time of Huss's first involvement with the chapel, tension is heightened by the return from Oxford of his young friend Jerome of Prague. Jerome brings with him books by John Wycliffe, whose views - particularly on the unholy nature of the papacy - coincide with those of Huss.

For several heady years the reformers preach and agitate in Prague. The papacy is an easy target. Since 1378 there have been two rival popes. From 1409 there are three. One of them even has the effrontery to sell indulgences in Prague to finance his campaign against his opponents.

Eventually a council is called at Constance, in 1414, to resolve the issue of the three popes. As a prominent voice in the argument for ecclesiastical reform, Huss is invited to Constance to put his case.

The invitation poses evident personal danger to Huss, but he is reassured by a promise of safe conduct from the emperor Sigismund. Huss bravely sets off for the small German town which is now the scene of a glittering assembly of Christian potentates. Within weeks of his arrival he is arrested, with the emperor's tacit approval.

The Council of Constance: 1414-1417

The council deals with the matter of heresy more speedily than it succeeds in reducing three popes to one. The ideas of Wycliffe and Huss are discussed and rapidly condemned. Huss is burnt at the stake in July 1415. By that time Jerome of Prague has with equal courage travelled to Constance to defend his master. He too is arrested. In May 1416 he is burnt on the same patch of ground as Huss.

To ensure that there are no relics of heresy, the council has Huss's ashes scattered in the Rhine. And it orders that Wycliffe's body be dug up, burnt and consigned to an English river.

The Hussite cause: 1415-1433

When news reaches Prague of Huss's death, burnt at the stake in Constance, the movement for reform is greatly strengthened. His successor as preacher in the Bethlehem chapel lists four radical principles upon which the Hussites insist.

The Four Articles of Prague demand: the freedom to preach; the wine as well as the bread to be given to the congregation in the mass; a clergy committed to poverty, together with the expropriation of church property; and the public punishment of notorious sinners, among whom prostitutes are singled out for special attention. The Hussites also differ from Rome in conducting their services in Czech rather than Latin.

These ideas spread rapidly through Bohemia, fuelled by a nationalist wave of anti-German sentiment. Germans are prosperous and influential in Bohemia. Huss was killed by a council on German soil. The man who betrayed his trust, revoking the promised safe conduct, is the German king and Holy Roman emperor Sigismund.

Sigismund is the half-brother of the Bohemian king Wenceslas IV. On the death of Wenceslas, in 1419, Sigismund presses his claim to the throne of Bohemia. The kingdom erupts.

In 1420 the Hussites build a fortified town at Tabor, on a bluff above a river about 50 miles south of Prague. From here their leader, Jan Zizka, conducts a series of brilliant campaigns against the armies of Sigismund and the new pope, Martin V.

The pope proclaims, in 1420, a crusade against the Hussites. It is not the first crusade against fellow Christians who are judged to be heretics (the Albigensian crusade is two centuries earlier). But it is the first time the heresy is specifically an attack on Roman Catholic practice, arguing that the papacy betrays the example of the early Christians in two ways - in its worldliness and in its restriction of the sacrament.

Marching under their symbolic banner (which displays a communion chalice), the Hussites defeat half a dozen papal and imperial armies sent against them between 1420 and 1431. They fight with the zeal of nationalism and piety. They benefit too from a military tactic pioneered by Zizka - his so called 'war wagon fortress', using farm wagons as mobile barricades behind which an attacking force can shelter (an idea more familiar, subsequently, in the Wild West, but also used by Babur in India in 1526).

These victories eventually wring from the papacy some notable concessions to Bohemia, in terms agreed in 1433.

Hussites established: 1433-1458

By the Compacts of Prague, agreed in 1433 and confirmed at a peace treaty in 1436, the Hussites are granted papal permission to give the sacrament in both kinds; their seizure of church lands in their territories is authorized; and Bohemia is granted an independent church under an elected arcbhishop.

These major concessions do not end the argument. The religious split remains the chief issue throughout the 15th century - which even sees the election of a Hussite king, George of Podebrady, to the Bohemian throne in 1458.

Devotio moderna and Erasmus: 15th - 16th century

During the 15th century there develops in northwest Europe a quiet devotional strain of Christianity so different from the pomp and ceremony of Rome that it seems, with hindsight, part of the complex thread evolving as the Reformation. But its practitioners would be horrified to see themselves in any such confrontational guise.

Known as devotio moderna, the movement derives from the Brethren of the Common Life - a group of both laymen and priests who share a simple life in imitation of the early Christians, devoting themselves to teaching and care of the poor.

A book written during the early 15th century - the Imitation of Christ, probably by Thomas à Kempis - becomes the extremely influential manual for Christian devotion of this kind. Without hierarchy and ritual, the emphasis in such a group is on the personal approach to Christ through the intense study of early Christian texts.

Such texts, originally in Greek, have in recent centuries been familiar only in the Latin of the Vulgate. In trying to go back to the early sources, these northern scholars share an interest with the pioneers of the Renaissance in Italy.

The education of Erasmus in the Netherlands in the 1470s is tinged with the influence of the devotio moderna. Like the brethren he can be seen as part of the trend towards the Reformation, though he strenuously avoids endorsing it.

His attitude to the materialistic papacy of the early 16th century (as seen in Julius Exclusus, a satirical play probably from his pen) is essentially that of the reformers. His careful edition of the Greek New Testament is in keeping both with devotio moderna and the Reformation - though one significant distinction remains. Erasmus translates the Greek in 1516 into Latin. Luther, just six years later, translates it into German.